Magnolia tree question
Last fall I planted two magnolia trees in my yard (a royal star and a Jane). They survived the winter and bloomed beautifully in the spring. They were doing great until a couple weeks ago. The royal stars leaves are turning brown and falling off. It looks like it might be dying. It is covered in Japanese beetles. Could they be killing my tree? If so, how can I get rid of them? Are there any suggestions on how I can save this tree? Thank you, Jessica
Hennepin County Minnesota
Your pictures do not show the telltale signs of Japanese beetles which are skeletonized leaves or total defoliation. One of the easiest ways to remove Japanese beetles from your trees is to shake them off into jars filled with soapy water. Carbaryl, acephate, pyrethrins, and pyrethroids and permethrin are insecticides that can be used to control adult Japanese beetles.
Magnolia should be planted in the full sun in moist, well drained, slightly acid soil. Iron chlorosis may occur on Magnolias grown in alkaline soil. http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/iron-chlorosis/
Trees often require several years to become established. The size of the root balls of your trees may have 10-50% of the original root system. Their small root systems are unable to take in enough water. Your trees may be showing transplant shock due to the hot summer temperatures. Magnolia do not tolerate dry soil. Newly planted plants require routine watering during the first three years. Typically, 5-7 gallons, applied to the root ball once a week is enough. A slow trickle of the garden hose at the base of the plant for several hours or until the soil is thoroughly soaked is the best method. Short, frequent watering should be avoided as this does not promote deep root growth but rather, the development of a shallow root system that is vulnerable to several environmental stresses. A 3- 4inch layer of wood chip mulch, spread to form a 3-6 foot diameter circle around the plant, should be applied. Keep the mulch material from direct contact with the tree trunk.
Examine the branches of your tree for tiny insects called Magnolia scale, Neolecanium cornuparvum. http://ohioline.osu.edu/factsheet/ENT-61